As shown in FIG. 1, a conventional 183/4" well head (2) will usually be mounted on a casing (4) having the dimension of 185/8" or 20". Such a casing will not have a pressure integrity equal to that of the well head, and it is therefore necessary to use new casings (6) having higher pressure integrity later in the well, which must be tied back to the high pressure well head in order for the well to have the same pressure integrity as said well head. According to conventional technique this will be provided by using so-called casing hangers (8) with associated gaskets between casing hangers and said well head. Normally there will be space for three casing hangers in a well head with associated gaskets and equipment therefor.
In order for such a conventional well head to be operable a lot of extra equipment is required. Such equipment will involve:
casing hangers, PA1 pack of assemblies, seal assemblies, PA1 wear bushings, one for each casing hanger, normally three pieces, PA1 running tool for casing hangers, universal tool and full bore casing hanger running tools, PA1 running tool for pack-off assembly/seal assembly, PA1 running tool for wear bushings, PA1 milling and flushing tools for seal assembly/pack-off assembly.